Method and apparatus for plating substrate with copper

ABSTRACT

The present invention relates to a method and apparatus for separating out metal copper according to an electroplating of copper using, for example, a solution of copper sulfate to produce copper interconnections on a surface of a substrate. The substrate is brought into contact, at least once, with a processing solution containing at least one of organic substance and sulfur compound which are contained in a plating solution. Thereafter, the substrate is brought into contact with the plating solution to plate the substrate.

[0001] This application is a Divisional Application of Ser. No.09/492,138 filed Jan. 27, 2000, now allowed.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a method and apparatus forseparating out metal copper according to an electroplating of copperusing, for example, a solution of copper sulfate in order to fill copperin fine interconnection grooves formed in a surface of a substrate suchas a semiconductor wafer to produce copper interconnections on thesurface of the substrate.

[0004] 2. Description of the Related Art

[0005] According to a conventional electroplating for plating asubstrate with copper using a solution of copper sulfate, a substrate isdipped in sulfuric acid or the like so as to be activated by the acid ina pre-treatment process outside of a plating tank. Instead of suchpre-treatment process, a substrate having a seed copper layer as anelectrically conductive layer may be brought into contact with asolution of copper sulfate in the plating tank. A thin surface Cu layeretching without electrical current loading (de-energization) can be madefor a certain period of time (activating time) in a pre-treatmentprocess. Then, an electric current is supplied to separate out metalcopper on the substrate after the pre-treatment process.

[0006] The former pre-treatment process is disadvantageous in that atank different from the plating tank is necessary to carry out thepre-treatment process. Hence, the required facility is large and therunning cost is increased.

[0007] On the other hand, the latter pre-treatment process isdisadvantageous in that the plating solution and the seed copper layeron the substrate are not brought into contact with each other underconstant conditions. Hence, additives such as a copper separationaccelerator and a copper separation inhibitor contained in the platingsolution tend to suffer initial adsorption irregularities to the surfaceof the seed copper layer and activation irregularities thereof. Further,the substrate is susceptible to the specific adsorption of a componentcaused by a black film on a soluble anode positioned in confrontingrelation to the substrate. As a consequence, the metal copper isabnormally separated out locally on the surface of the substrate,causing the substrate to have a stained appearance. When the metalcopper is nonuniformly and abnormally separated out locally, the crystalorientation of the copper and the thickness of the copper layer becomeirregular, making it difficult for the substrate to be polished to aflat finish by a chemical mechanical polishing (CMP) process after theplating process.

[0008] According to conventional solutions to the above problems, theactivating time is increased, or the substrate is rotated or the platingsolution is stirred by a device known as a squeegee, whereby adsorptionirregularities and activation irregularities are eliminated. However,the activating process carried out for a long period of time tends todissolve away the seed copper layer in its entirety because the seedcopper layer provided as a fine interconnection pattern or a very thinelectrode layer on the bottom of holes having a high aspect ratio isetched more than other portions, possibly making it impossible to embedmetal copper according to electroplating. The other solutions referredto above are disadvantageous in that they make the entire system complexor large in size.

[0009] Further, the conventional copper plating process is problematicin that the thickness of the deposited copper film differs from locationto location because of the presence of the interconnection pattern.According to this problem, specifically, the thickness of the depositedcopper film is much larger in an area where fine interconnections areclosely spaced than in an area which is free of fine interconnections.The hump, which is the difference between the thickness of the depositedcopper film in the area where fine interconnections are closely spacedand the thickness of the deposited copper film in the area free of fineinterconnections, may reach 1 μm. The hump presents difficulty inpolishing the deposited copper film to a flat finish in the chemicalmechanical polishing (CMP) process subsequent to the plating process.Any undesirable remaining copper film in the area where fineinterconnections are closely spaced tends to cause a short circuitbetween the interconnections. Thus, the yield of substrates is likely tobe lowered.

SUMMARY OF THE INVENTION

[0010] It is therefore an object of the present invention to provide amethod and apparatus for plating a substrate with copper which canprevent metal copper from being separated out locally on the surface ofthe substrate, allow a plated copper film to be easily planarized in achemical mechanical polishing (CMP) process after the plating process,and finish the substrate to a mirror-like glossy surface with arelatively simple facility and a process.

[0011] In order to achieve the above object, according to one aspect ofthe present invention, there is provided a method for plating asubstrate with copper, comprising: bringing, at least once, a substrateinto contact with a processing solution containing at least one oforganic substance and sulfur compound which are contained in a platingsolution; and bringing the substrate into contact with the platingsolution to plate the substrate.

[0012] The substrate is brought into contact with the processingsolution before the substrate is plated and/or while the substrate isbeing plated. The phrase “while the substrate is being plated” meanswhile the plated film is being deposited in a stage before the thicknessof the plated film reaches a final target thickness for the plated film.

[0013] In the above plating method, before the substrate is plated, thesubstrate is brought into contact with the processing solution whichcontains at least one of an organic substance and a sulfur compoundwhich are contained in the plating solution. Alternatively, after theplating solution is removed from the substrate by interrupting platingof the substrate, the substrate is brought into contact with theprocessing solution.

[0014] The substrate may be brought into contact with the processingsolution by directly dipping the substrate into the processing solutionin a tank, spraying the processing solution over the substrate while thesubstrate is being rotated in a horizontal plane at a high speed as witha spin dryer, or supplying the processing solution by a pump into adedicated dipping chamber in which the substrate is set at apredetermined position. When the substrate is thus brought into theprocessing solution, a thin film of the organic substance and/or thesulfur compound is coated on the processed surface of the substrate.Extra processing solution is preferably removed from the substrate, andthen the substrate is plated with copper according to a conventionalprocess. In this manner, metal copper is prevented from being separatedout locally on the processed surface of the substrate, and the substrateis plated to provide a mirror-like glossy surface. Further, the size ofhumps in an area of closely spaced interconnections on the processedsurface of the substrate can be suppressed.

[0015] Thereafter, it is preferable to remove the processing solutionfrom the substrate and/or to dry the substrate to minimize any amount ofprocessing solution carried into the plating solution to maintain abetter quality of the plating solution. However, since the amount ofprocessing solution which is coated is usually much smaller than theamount of plating solution, removing the processing solution from thesubstrate and/or drying of the substrate are not necessarily required.The processing solution may be removed from the substrate by simplylowering the level of processing solution, lifting the substrate out ofthe processing solution, rotating the substrate to spin off theprocessing solution from the substrate as with a spin dryer, rotatingthe substrate and applying a nitrogen gas blow to the substrate, orpassing the substrate through a forced air flow such as an air blower.Further, the two processes including removing of the processing solutionand drying of the substrate may be performed successively by oneapparatus. For example, the processing solution may be sprayed over thesubstrate while the substrate is being rotated by a spin cleaner/dryeror the like. This method allows the substrate to contact the processingsolution and also allows the processing solution to be removed from thesubstrate.

[0016] The processing solution may be continuously removed from thesubstrate until the substrate is dried to a certain extent for therebyfurther minimizing the amount of processing solution carried into theplating solution. In this case, it is preferable to dry the substrate toa partly dried state with a certain moisture content, rather than fullydrying the substrate.

[0017] The mechanism of the present invention, though it is not fullyelucidated, is as follows. The organic substance used in the presentinvention, which is contained in the plating solution, is known to beeffective in offering surface activity and suppressing theseparating-out of copper for uniform electrodepositability. The sulfurcompound, which is contained in the plating solution, is known to beeffective in increasing the separating-out of copper to make the crystalof the separated-out film fine for thereby increasing the glossy levelof the plated film. By coating a thin layer of the organic substanceand/or the sulfur compound on the processed surface of the substrate inadvance and/or while the substrate is being plated, the separating-outof copper over the substrate in its entirety is uniformly accelerated orsuppressed, and any abnormal separating-out of copper is prevented. Thiseffect remains the same after the substrate is dried to a certainextent.

[0018] Moreover, the organic substance or the sulfur compound in theplating solution is effective to increase wettability between theplating solution and the processed surface of the substrate. Even afterthe substrate is dried to a certain extent, this effect of the organicsubstance or the sulfur compound remains the same because the organicsubstance or the sulfur compound is eluted into the plating solution.Therefore, wetting between the plating solution and the processedsurface of the substrate is improved and made uniform over its entiresurface, allowing the entire surface of the substrate to be plateduniformly and efficiently. These advantages lead to an improvement ofthe embeddability of plated copper into high aspect ratio holes andgrooves on the substrate.

[0019] The organic substance preferably comprises polyethers in anorganic polymer for use in copper plating processes. Experiences intests conducted by the inventors indicate that the organic substance hasa concentration ranging from 10 mg/l to 10 g/l in the processingsolution and a molecular weight ranging from 100 to 100,000. The organicsubstance may be a copolymer or a block polymer such as polyethyleneglycol, polypropylene glycol, polyvinyl alcohol, ethoxy-naphthol,propoxy-naphthol, ethoxy-phenol, propoxy-phenol, polyoxyethylenepolyoxypropylene block polymer, ethoxy-nonylphenol,carboxymethylcellulose, or polyethylene proplylene glycol. Theprocessing solution containing the organic substance is particularlyeffective as a pre-treatment solution for use prior to the platingprocess.

[0020] The sulfur compound is represented by the following generalformula:

X-L-(S)_(n)-L-X

[0021] where L represents a lower alkyl group, a lower alkoxy group, ahydroxyl group, or an alkyl group replaceable with a halogen atom andhaving a carbon number ranging from 1 to 6, X represents a hydrogenatom, an SO3M group, or a PO3M group where M indicates a hydrogen atom,an alkaline metal, or an amino group. The processing solution containingthe sulfur compound is highly effective to accelerate the separating-outof copper in fine interconnections and suppress humps on the substrate.It is particularly effective that the sulfur compound has aconcentration ranging from 0.1 μmol/l to 70 μmol/l in the processingsolution.

[0022] The substrate and the processing solution may be held in contactwith each other for a period of time sufficient to cause the processingsolution to contact the entire surface of the substrate. If the periodof time were too long, the current supplying layer (seed layer) would bechemically damaged. Usually, the period of time is selected in the rangefrom 3 to 60 seconds. If the processing solution is strongly alkaline,then the hydrolysis of the organic substance and the sulfur compoundtends to progress. If the acidity of the processing solution is toostrong, then the copper of the seed layer is liable to be etched. Forthis reason, the pH of the processing solution is preferably in therange of 2 to 9. Depending on the type of plating apparatus used, adried or partly dried substrate may be needed. In such a case, the aboveeffect is unchanged even if the substrate is dried after the substrateand the processing solution are brought into contact with each other.

[0023] The method may further comprise etching the plated film at leastonce by interrupting plating of the substrate while the substrate isbeing plated, and the substrate is brought into contact with the platingsolution again to plate the substrate after the plated film is etched.If the plated film is etched by interrupting plating of the substratewhile the substrate is being plated, then the plated film may be etchedby an electrolytic etching process in which the current is passed in adirection opposite to the direction in normal plating, or a chemicaletching process in which sulfuric acid is employed. Further, after theetching process, the process for bringing, at least once, the substrateinto contact with the processing solution may be performed, and then thesubstrate may be brought into contact with the plating solution again toplate the substrate.

[0024] The current supplied in the electrolytic etching process may be adirect current or a pulsed current (so-called PR pulse). The etcheddepth is proportional to the supplied amount of current (the product ofthe magnitude of the current and the time in which the current ispassed). The current is supplied to the substrate at a current densityranging from 1 to 30 mA/cm2 for a period of time ranging from about 0.5to 30 seconds. The concentration of sulfuric acid employed in thechemical etching process is preferably in the range of about 0.5 to 30%,and the substrate is held in the sulfuric acid for a period of timeranging from about 1 to 30 seconds. The sulfuric acid is a most popularadditive added to the plating solution, and can easily be handled fromthe standpoint of the composition management of the plating solution.The thickness of the plated film that is etched away is 1 nm or more forachieving any appreciable effect of the etching process, and ispreferably in the range of about 10 to 50 nm.

[0025] According to another aspect of the present invention, there isprovided an apparatus for plating a substrate with copper, comprising: adevice for bringing a substrate into contact with a processing solutioncontaining at least one of an organic substance and a sulfur compoundcontained in a plating solution; and a device for bringing the substrateinto contact with the plating solution to plate the substrate.

[0026] According to still another aspect of the present invention, thereis also provided an apparatus for plating a substrate with copper,comprising: a device for bringing a substrate into contact with aprocessing solution containing at least one of an organic substance anda sulfur compound contained in a plating solution; a device for bringingthe substrate into contact with the plating solution to plate thesubstrate; and a device for etching a plated film deposited on thesubstrate.

[0027] A processing tank for bringing the substrate into contact withthe processing solution therein may be separate from a plating tank forplating the substrate, or one common tank may be used instead of thesetwo tanks. If the two tanks are separately employed, then these tanksmay be positioned closely to each other, with a delivery unit providedfor quickly delivering substrates to the tanks. If one common tank isemployed, then the tank may be combined with supply passages forindividually supplying the processing solution and the plating solution,and drain passages for changing the solutions. The apparatus may furthercomprise a device for spraying the processing solution over thesubstrate while the substrate is being rotated, thereby to bring theprocessing solution into contact with the substrate. Therefore, therotational speed of the substrate is increased to remove the processingsolution from the substrate and/or to dry the substrate.

[0028] The apparatus may further include, in addition to the processingtank and the plating tank, a loading and/or unloading unit for loadingand/or unloading substrates, a transferring device for transferringsubstrates, a cleaning unit for cleaning substrates, and a drying unitfor drying substrates, so that substrates can be loaded and unloaded ina clean condition.

[0029] The above and other objects, features, and advantages of thepresent invention will become apparent from the following descriptionwhen taken in conjunction with the accompanying drawings whichillustrates preferred embodiments of the present invention by way ofexample.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030]FIG. 1 is a schematic plan view of a plating apparatus accordingto an embodiment of the present invention;

[0031]FIG. 2 is a schematic plan view of a plating apparatus accordingto another embodiment of the present invention; and

[0032]FIG. 3 is a schematic plan view of a plating apparatus accordingto still another embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0033] Next, a method and apparatus for plating a substrate with copperaccording to an embodiment of the present invention will be describedbelow with reference to FIG. 1.

[0034] As shown in FIG. 1, a plating apparatus 1 comprises a loadingunit 4 and an unloading unit 5 for loading and unloading wafer cassettes(not shown) housing substrates (not shown) such as semiconductor wafersto be processed, a delivery arm 8 and a movable delivery arm 9 fordelivering substrates one at a time, a pair of coating tanks (processingtanks) 2 for processing the surface of a substrate with a processingsolution, a plurality of plating tanks 3 for plating substrates, acleaning unit 6 for cleaning substrates, and a pair of rinsing anddrying units 10 for rinsing and drying substrates. Each of the coatingtanks 2 and the plating tanks 3 may be a batch-type tank for processinga plurality of substrates simultaneously, or may be an individualprocessing tank for processing substrates individually one at a time.Further, each of the coating tanks 2 and the plating tanks 3 may be adip-type tank for steadily holding a plating solution or a processingsolution, or a tank for being supplied with and discharging a platingsolution or a processing solution each time a plurality of substrates ora substrate is processed. The delivery arm 8 is used to handle cleansubstrates, and the movable delivery arm 9 is used to deliver substratesto be plated or processed.

[0035] A process of plating a substrate (not shown) with the platingapparatus 1 shown in FIG. 1 will be described below with respect to aprocessing flow for one of the substrates. First, a wafer cassettehousing, where the substrates are put in, is set in the loading unit 4.Then, the delivery arm 8 takes out a substrate from the wafer cassette,and transfers the substrate to a loading stage 7. The movable deliveryarm 9 receives the substrate from the loading stage 7, and places thesubstrate into one of the coating tanks 2 which hold a processingsolution 12 a containing at least one of an organic substance and asulfur compound contained in a copper plating solution. After thesubstrate is pre-treated by being dipped in the processing solution 12 afor a certain period of time, the processed substrate is removed fromthe coating tank 2 by the movable delivery arm 9, and then placed intoone of the plating tanks 3 holding a plating solution 13. In the platingtank 3, the substrate is electrically plated with copper.

[0036] If the size of a hump on the substrate needs to be suppressed,then the electric current supplied to the plating tank 3 is stopped tointerrupt the copper plating process before the deposited copper filmreaches a desired film thickness in the plating tank 3. When thedeposited copper film is to be electrolytically etched at this time,then the copper plating process is interrupted, and the electric currentis passed in a direction opposite to the direction in which it waspassed in the copper plating process. A desired current quantity, whichis represented by the product of the magnitude of the current and theamount of time during which the current is passed, is given to etch thedeposited copper film.

[0037] Thereafter, if necessary, the substrate is removed from theplating tank 3 by the movable delivery arm 9, and placed into the othercoating tank 2 which holds a coating solution 12 b containing at leastone of an organic substance and a sulfur compound contained in a copperplating solution. The substrate is coated by dipping the substrate inthe coating solution 12 b for a predetermined period of time. In thiscase, if the processing solutions 12 a, 12 b have the same composition,then only one of the coating tanks 2 may be used to process and coat thesubstrate. Thereafter, the movable delivery arm 9 removes the coatedsubstrate from the coating tank 2, and places the substrate into one ofthe plating tanks 3 holding the plating solution 13 for electricallyplating the substrate with copper for a remaining film thickness.

[0038] After the completion of the plating process, the movable deliveryarm 9 removes the plated substrate from the plating tank 3, and placesthe substrate on the cleaning unit 6 where the substrate is cleaned in aprimary cleaning stage. Then, the delivery arm 8 removes the substratefrom the cleaning unit 6 and transfers the substrate to the rinsing anddrying unit 10 where the substrate is cleaned in a secondary cleaningstage and then dried. The dried substrate is transferred from therinsing and drying unit 10 to the wafer cassette in the unloading unit 5by the delivery arm 8. The substrates in the wafer cassette are thenunloaded as clean plated substrates, and sent to the next process suchas a CMP process. The plating apparatus 1 has a plurality of coatingtanks 2 and a plurality of plating tanks 3, and the delivery arm 8 andthe movable delivery arm 9 are controlled and programmed to processsubstrates successively and efficiently in the coating tanks 2 and theplating tanks 3. Therefore, the plating apparatus 1 has a high operatingefficiency.

[0039]FIG. 2 shows a plating apparatus 1 according to another embodimentof the present invention. The plating apparatus 1 shown in FIG. 2 isessentially the same as the plating apparatus 1 shown in FIG. 1 exceptthat rotary processing units 11 are employed to process substrates. Eachof the rotary processing units 11 comprises a holder mechanism forrotating a substrate, and a spray nozzle for spraying a processingsolution over the surface of the substrate. The processing solutionsprayed from the spray nozzle onto the substrate can be spread uniformlyover the surface of the substrate when the substrate is rotated. Afterthe supply of the processing solution is stopped, the substrate isrotated at an increased speed to remove excess processing solution fromthe substrate and to dry the substrate in a continuous manner.Therefore, the surface of the substrate can be uniformly coatedefficiently with the processing solution, dried, and plated with adesired film of copper.

[0040]FIG. 3 shows a plating apparatus 1 according to still anotherembodiment of the present invention. The plating apparatus 1 shown inFIG. 3 has substantially the same structure as the plating apparatusshown in FIG. 2, and has a plurality of processing tanks 3, 10, 11 and asingle loading and unloading unit 14 for loading and unloadingsubstrates, which are disposed around a single delivery arm 8. Thedelivery arm 8 delivers substrates to and from the processing tanks 3,10, 11 and the loading and unloading unit 14. The layout of theprocessing tanks 3, 10, 11 and the loading and unloading unit 14disposed around the delivery arm 8 can reduce an installation space ofthe plating apparatus. The plating apparatus 1 shown in FIG. 3 iscapable of depositing a desired layer of copper on a substrate anddischarging it as a clean plated substrate therefrom, as with theplating apparatus 1 according to the previous embodiments.

[0041] Examples of the plating process carried out by the above platingapparatus will be described below.

EXAMPLE 1

[0042] Example 1 had the following processing conditions:

[0043] (1) Processing Solution:

[0044] 1) Polypropylene glycol (PPG, molecular weight: 400,concentration: 10 mg/l and 5 g/l);

[0045] 2) Polyethylene glycol (PEG, molecular weight: 20,000,concentration: 100 mg/l and 10 g/l);

[0046] 3) Mixed solution of 1) and 2) (PPG: molecular weight: 700,concentration: 50 mg/l, PEG: molecular weight: 6,000, concentration: 50mg/l).

[0047] (2) Substrate used:

[0048] After a thermal oxide film was deposited to a thickness of 100 nmon an 8-inch silicon substrate, a p-SiN film was deposited as an etchingstopper to a thickness of 50 nm on the thermal oxide film. Thereafter, aTEOS oxide film was deposited to a thickness of 600 nm on the p-SiNfilm. On the substrate, a TaN film having a thickness of 20 nm wasdeposited as a barrier metal for copper interconnections by reactivesputtering, after which a seed layer having a thickness of 150 nm forcopper plating was continuously deposited without breaking the vacuum byan LTS (long-throw sputtering) process.

[0049] (3) Processing time:

[0050] The substrate was dipped in the processing solution for 10seconds.

[0051] (4) Drying process:

[0052] Spin dryer (Rotational speed: 3,000/min. (30 seconds, no nitrogengas blow)

[0053] (5) Test results:

[0054] Five substrates processed by the above processing solutionscontaining organic substances and an unprocessed substrate (comparativeexample) were plated in an individual processing dip-type plating tank3. The plating solution was a copper plating solution composed mainly ofcopper sulfate, and the plated copper film had a thickness of 500 nm.Appearances and CMP characteristics of the plated examples are shown inTable 1 below. TABLE 1 Organic CMP substances Concentration Appearancecharacteristics Run-1 PPG  10 mg/l Mirror fin- Bood ish, glossy Run-2PPG  5 g/l Mirror fin- Good ish, glossy Run-3 PEG 100 mg/l Mirror fin-Good ish, glossy Run-4 PEG  10 g/l Mirror fin- Good ish, glossy Run-5PEG + PPG Total: 100 mg/l Mirror fin- Good ish, glossy Run-6 None NoneStained Bad (lack of (Comparative inter- example) connections)

[0055] Furthermore, the Cu concentration on the back of the substrateswas measured as reference data.

[0056] The measured Cu concentration of the unprocessed substrate was5×10¹² atm/cm², whereas the measured Cu concentration of each of theprocessed substrates was 5×10¹¹ atm/cm² or lower. This result indicatesthat the present invention is effective to reduce copper contaminationon the back of the substrate.

[0057] The present example was also found effective to prevent a portionof the current supplying layer where the copper film is very thin frombeing dissolved, resulting in the promotion of the separation of copperas a plated layer. The reason for this effect appears to be that thepolymer used in the present invention also functions as an inhibitor forinhibiting the copper of the current supplying layer from beingdissolved.

EXAMPLE 2

[0058] A substrate was pre-treated by a processing solution containing asulfur compound contained in a plating solution.

[0059] (1) Processing solution:

[0060] N, N-dimethyldithiocarbamyl propylsulfonic acid (concentration:30 μmol/l)

[0061] (2) Substrate used:

[0062] After a thermal oxide film was deposited to a thickness of 100 nmon an 8-inch silicon substrate, a p-SiN film was deposited as an etchingstopper to a thickness of 50 nm on the thermal oxide film. Thereafter, aTEOS oxide film was deposited to a thickness of 1,000 nm on the p-SiNfilm. Holes having a diameter of 0.25 μm and an aspect ratio of 4 andholes having a diameter of 0.5 μm and an aspect ratio of 2 were formedin the TEOS oxide film according to an ordinary lithographic process andan oxide film etching process. On the substrate, a TaN film having athickness of 20 nm was deposited as a barrier metal for copperinterconnections by reactive sputtering, after which a seed layer havinga thickness of 150 nm for copper plating was continuously depositedwithout breaking the vacuum by an LTS (long-throw sputtering) process.Thereafter, the substrate was brought into contact with the aboveprocessing solution, and then a current was supplied via the copper seedlayer to plate the substrate with copper in a plating solution composedmainly of copper sulfate. Another substrate which was not brought intocontact with the above processing solution was also plated in the samemanner. The plated copper film had a thickness of 600 nm. After theplating process, an embedded state in the holes was observed byobserving a cross-section with a SEM (scanning electron microscope).

[0063] (3) Processing time: The substrate was dipped in the processingsolution for 5 seconds.

[0064] (4) Drying process:

[0065] Spin dryer (Rotational speed: 2,000/min. (30 seconds, no nitrogengas blow)

[0066] (5) Test results:

[0067] The results are shown in Table 2 below. The holes, which had adiameter of 0.5 μm and an aspect ratio of 2, in the substrates processedby the sulfur compound solution and not processed by the sulfur compoundsolution exhibited no difference. The hole which had a diameter of 0.25μm and an aspect ratio of 4 in the substrate processed by the sulfurcompound solution was filled without voids, but the hole which had adiameter of 0.25 μm and an aspect ratio of 4 in the substrate notprocessed by the sulfur compound solution suffered voids in the bottomthereof. The processing based on the sulfur compound solution isconsidered to accelerate the deposition of plated copper on the bottomof the hole. TABLE 2 Hole having a diameter Hole having a diameter of0.5 μm and an of 0.25 μm and an aspect ratio of 2 aspect ratio of 4 Notprocessed by Large voids at the Small voids at the bottom sulfurcompound Bottom of the hole of the hole solution Processed by sulfurFully filled Fully filled compound solution

EXAMPLE 3

[0068] A substrate was pre-treated by a processing solution containingan organic substance and a sulfur compound contained in a platingsolution.

[0069] (1) Processing solution:

[0070] 1) Organic substance: Mixed solution of PPG and PEG (PPG:molecular weight: 700, concentration: 50 mg/l, PEG: molecular weight:6,000, concentration: 50 mg/l).

[0071] 2) Sulfur compound: N,N-dimethyldithiocarbamyl propylsulfonicacid (concentration: 70 μmol/l)

[0072] (2) Substrate used:

[0073] After a thermal oxide film was deposited to a thickness of 100 nmon an 8-inch silicon substrate, a p-SiN film was deposited as an etchingstopper to a thickness of 50 nm on the thermal oxide film. Thereafter, aTEOS oxide film was deposited to a thickness of 1,000 nm on the p-SiNfilm. Holes having a diameter of 0.20 μm and an aspect ratio of 5 andholes having a diameter of 0.30 μm and an aspect ratio of 4 were formedin the TEOS oxide film according to an ordinary lithographic process andan oxide film etching process. On the substrate, a TaN film having athickness of 20 nm was deposited as a barrier metal for copperinterconnections by reactive sputtering, after which a seed layer havinga thickness of 150 nm for copper plating was continuously depositedwithout breaking the vacuum by an LTS (long-throw sputtering) process.Thereafter, the substrate was brought into contact with the aboveprocessing solution, and then a current was supplied via the copper seedlayer to plate the substrate with copper in a plating solution composedmainly of copper sulfate. Another substrate which was not brought intocontact with the above processing solution was also plated in the samemanner. The plated copper film had a thickness of 600 nm. After theplating process, an embedded state in the holes was observed byobserving a cross-section with a SEM (scanning electron microscope).

[0074] (3) Processing time:

[0075] The substrate was rotated at a rotational speed of 150 rpm by aspin dryer and the solution was supplied at a rate of 10 ml/second.

[0076] (4) Drying process:

[0077] Spin dryer (Rotational speed: 2,000/min. (30 seconds, no nitrogengas blow)

[0078] (5) Test results:

[0079] The results are shown in Table 3 below. The holes, which had adiameter of 0.30 μm and an aspect ratio of 4, in the substratesprocessed by the sulfur compound solution and not processed by thesulfur compound solution exhibited no difference. The hole which had adiameter of 0.20 μm and an aspect ratio of 5 in the substrate processedby the sulfur compound solution was filled without voids, but the holewhich had a diameter of 0.20 μm and an aspect ratio of 5 in thesubstrate not processed by the sulfur compound solution suffered voidsin the bottom thereof. The organic substance is considered to haveincreased the wettability and the uniform electrodepositability in theholes, and the processing based on the sulfur compound solution isconsidered to accelerate the deposition of plated copper on the bottomof the hole. TABLE 3 Hole having a diameter Hole having a diameter of0.20 μm and an of 0.30 μm and an aspect ratio of 5 aspect ratio of 4 Notprocessed by Large voids at the Small voids at the bottom organicsubstance Bottom of the hole of the hole and sulfur com- pound solutionProcessed by organ- Fully filled Fully filled ic substance and sulfurcompound solution

EXAMPLE 4

[0080] While a substrate was being plated with copper, the surface ofthe plated copper film was brought into contact with a processingsolution containing a sulfur compound contained in a copper platingsolution, or the surface of the plated film was etched.

[0081] (1) Substrate used:

[0082] After a thermal oxide film was deposited to a thickness of 100 nmon an 8-inch silicon substrate, a p-SiN film was deposited as an etchingstopper to a thickness of 50 nm on the thermal oxide film. Thereafter, aTEOS oxide film was deposited to a thickness of 1,000 nm on the p-SiNfilm. A groove pattern having a width of 0.2 μm with 0.2 μm wide spaceand an aspect ratio of 3 was formed in the TEOS oxide film according toan ordinary lithographic process and an oxide film etching process. Onthe substrate, a TaN film having a thickness of 20 nm was deposited as abarrier metal for copper interconnections by reactive sputtering, afterwhich a seed layer having a thickness of 150 nm for copper plating wascontinuously deposited without breaking the vacuum by an LTS (long-throwsputtering) process. Thereafter, a current was supplied via the copperseed layer to plate the substrate with copper in a plating solutioncomposed mainly of copper sulfate. The plated copper film had athickness of 500 nm (650 nm including the thickness of the copper seedlayer).

[0083] (2) Processing instance 1.

[0084] The copper plating process was stopped when the plated copperfilm was deposited to a thickness of 100 nm, and the plating solutionwas removed from the surface of the plated copper film. Thereafter, thesurface of the plated copper film was brought into contact with aprocessing solution in which a sulfur compound(N,N-dimethyidithiocarbamyl propylsulfonic acid (concentration: 5mg/l=24 μmol/l)) contained in the plating solution was dissolved.Subsequently, the surface of the plated copper film was brought intocontact with the plating solution again, and copper was deposited to aremaining thickness of 400 nm by electroplating.

[0085] (3) Processing instance 2:

[0086] The copper plating process was stopped when the plated copperfilm was deposited to a thickness of 100 nm, and the anode and thecathode for electroplating were switched around and currentscorresponding to etched copper film thicknesses of 10 nm (processinginstance 2-1), 20 nm (processing instance 2-2), and 30 nm (processinginstance 2-3) were supplied. Thereafter, the plating solution wasremoved from the surface of the plated copper film. The surface of theplated copper film was brought into contact with a processing solutionin which a sulfur compound (N, N-dimethyidithiocarbamyl propylsulfonicacid (concentration: 5 mg/l=24 μmol/l)) contained in the platingsolution was dissolved. Subsequently, the surface of the plated copperfilm was brought into contact with the plating solution again, and theanode and the cathode for electroplating were switched around and copperwas deposited to a remaining thickness of 400 nm by electroplating.

[0087] (4) Processing instance 3:

[0088] The copper plating process was stopped when the plated copperfilm was deposited to a thickness of 100 nm, and the anode and thecathode for electroplating were switched around and currentscorresponding to etched copper film thicknesses of 10 nm (processinginstance 3-1), and 30 nm (processing instance 3-2) were supplied.Thereafter, the anode and the cathode for electroplating were switchedaround and copper was deposited to a remaining thickness of 400 nm byelectroplating.

[0089] (5) Test results:

[0090] The shapes of the grooves filled by the plated copper films onthe substrates thus produced were observed by observing a cross-sectionwith SEM (scanning electron microscope), and the differences (the sizesof humps) between the thicknesses of the plated copper films on thegroove patterns and the thicknesses of the plated copper films on largespaces next to the groove patterns were checked. The results are shownin Table 4 below. Table 4 also includes the results of a comparativeexample in which a plated copper film having a thickness of 1,000 nm wasdeposited on a substrate. TABLE 4 Thickness of Thickness of platedcopper plated copper film on groove film on adjacent Hump Surfacepattern (nm) space (nm) size (nm) gloss Processing 700 625 75 Goodinstance 1 Processing 775 650 125 Good instance 2-1 (10 nm) Processing725 625 100 Good instance 2-2 (20 nm) Processing 700 625 75 Goodinstance 2-3 (30 nm) Processing 675 625 50 Good instance 3-1 (10 nm)Processing 700 625 75 Good instance 3-2 (30 nm) Comparative 1000 400 600Bad example

[0091] By bringing the surface of the plated copper film once intocontact with the processing solution containing the sulfur compoundcontained in the copper plating solution during the copper platingprocess or etching the plated copper film, the size of humps which wouldobstruct the planarization process such as the chemical mechanicalpolishing (CMP) process after the plating process can be greatlyreduced.

[0092] In this example, the processing solution contained the sulfurcompound contained in the copper plating solution. However, theprocessing solution may contain an organic substance contained in thecopper plating solution.

[0093] According to the present invention, as described above, sincecopper is prevented from being abnormally separated out while asubstrate is being plated with copper, the substrate can be plated witha copper film having a uniform thickness while reducing the size of anyundesirable humps. Copper can be embedded well for fineinterconnections, producing copper interconnections free of defects suchas voids. As a result, the plated substrate can subsequently be easilypolished by the chemical mechanical polishing process, so that the yieldof LSI circuits with copper interconnections can be increased.Therefore, the cost of LSI circuit fabrication can be greatly belowered. Accordingly, the method and the apparatus for plating asubstrate with copper according to the present invention are highlyuseful and effective in the industry of semiconductor fabrication.

[0094] In the above embodiments, although a method and apparatus forplating a substrate with copper have been described, the presentinvention is applicable to a method and apparatus for plating asubstrate with a different metal such as silver or gold.

[0095] Although certain preferred embodiments of the present inventionhave been shown and described in detail, it should be understood thatvarious changes and modifications may be made therein without departingfrom the scope of the appended claims.

What is claimed is:
 1. A method to fill a metal in fine grooves formedin a surface of a substrate, comprising: bringing the substrate intocontact with a plating solution; plating the substrate with the platingsolution electrically with an electric current to form a plated metalfilm; stopping the electric current to interrupt the plating before theplated metal film reaches a desired film thickness; etching the platedmetal film electrolytically with a direct electric current opposite tothe electric current during plating; and plating the substrate havingthe etched metal film to form a remaining film thickness to reach thedesired film thickness.
 2. A method according to claim 1, wherein acurrent density of the direct electric current during etching in a rangeof 1 mA/cm² to 30 mA/cm².
 3. A method according to claim 1, wherein thedirect electric current for performing etching is supplied for a periodof time in a range of about 0.5 seconds to 30 seconds.
 4. A methodaccording to claim 1, wherein said metal is copper.
 5. A methodaccording to claim 1, wherein the etching is performed with the platingsolution.
 6. A method according to claim 1, wherein the plating of thesubstrate having the etched metal film is performed with the platingsolution.
 7. A metal for plating a substrate with copper, comprising:bringing, at least once, a substrate into contact with a processingliquid offering surface activity of a substrate surface and/orincreasing wettability between a plating solution and the substratesurface; performing one of removing the processing liquid from thesubstrate and drying the substrate; and bringing the substrate intocontact with the plating solution to plate the substrate afterperforming one of removing the processing liquid from the substrate anddrying the substrate.
 8. A method according to claim 7, wherein saidperforming includes one of rotating the substrate to spin off theprocessing liquid from the substrate, rotating the substrate andapplying a gas below to the substrate, and passing the substrate througha forced air.
 9. A method according to claim 7, wherein said performingis successively performed after the substrate is brought into contactwith the processing liquid by one apparatus.